1. Field of the Invention
The present invention relates to a plasma processing technique for use in fabricating semiconductor devices and, more particularly to a plasma processing system for processing wafers, etc., by the use of plasma, a process monitoring method, and method for fabricating a semiconductor device.
2. Description of the Related Art
Plasma processing systems use a reactive gas plasma excited by radio frequency electric power to etch a thin film on a surface of a substrate or deposit a thin film on a surface of a wafer by generated ions and radicals, and are widely used in processes for fabricating semiconductor devices.
A conventional plasma processing system will be explained with reference to a parallel plate reactive ion etching system shown in FIG. 8.
An upper electrode 62 and a lower electrode 64 are positioned opposite to each other in a vacuum chamber 60 for plasma processing. A wafer 66 to be etched is mounted on the lower electrode 64. A radio frequency electric power supply 70 for generating a plasma 68 between the upper electrode 62 and the lower electrode 64 is applied between the upper and the lower electrodes 62, 64 through impedance matching unit 72. The vacuum chamber 60 includes a flow rate controller 74 for introducing a required rate of an etching gas, and a gas pressure controller 76. The radio frequency electric power supply 70, the flow rate controller 74 and the gas pressure controller 76 are connected to a computer for system control 78.
Then, the operation of the conventional plasma processing system will be explained.
First, a wafer 66 to be processed is mounted on the lower electrode 64 in the vacuum chamber 60, and then an internal pressure of the vacuum chamber 60 is reduced to a required pressure.
Next, an etching gas is introduced into the vacuum chamber 60 through the flow rate controller 74 while an internal pressure of the vacuum chamber 60 is maintained constant by the gas pressure controller 76.
Then, in this state a radio frequency is applied between the upper electrode 62 and the lower electrode 64 to generate a plasma 68 between the electrodes. The operating frequency supplied by the radio frequency electric power supply 70 is, e.g., 13.56 MHz.
Thus, the film on the wafer 66 mounted on the lower electrode 64 is etched by ions and radicals in the plasma into a required pattern.
For the etching, usually etching conditions (system control parameters), such as a radio frequency electric power, a gas pressure, and gas flow rate, are set in the computer for system control 78, so that associated controller separately retain set values.
However, a plasma condition, which affects properties of an etching process, such as etching rate, etc., is determined by the so-called condition setting, in which set values, as of radio frequency electric power, gas pressure, gas flow rate, etc., are variously changed to investigate the relationship between the set conditions and etching rate, uniformity, selectivity and processed profile, etc., and the set conditions are adjusted so that characteristics obtained by the plasma processing, e.g., etching rate, etching uniformity, selectivity, processed profile etc. become as required, whereby mass production conditions are determined.
That is, a plasma condition is determined by correlation among a radio frequency electric power, a gas pressure, a gas flow rate, etc., and by separately controlling respective plasma parameters a plasma condition cannot be directly controlled. Accordingly, the conventional plasma processing system in which a radio frequency electric power, a gas pressure, a gas flow rate, etc., are separately controlled by the associated controller controlled by the computer for system control 78 cannot suitably control the plasma condition.
In the usual plasma processing system, for ends of TAT (turnaround time) improvement, etc., characteristics provided by processing are periodically checked by a line operator for in-line administration, but wafers are not checked one-by-one as to whether or not the processing is normally conducted.
As a result, it is accordingly impossible to check changes of processing characteristics, such as etching characteristics, caused by transient changes of the electrode surfaces and wall of the vacuum chamber 60 caused by increased numbers of processed wafers, fluctuation and troubles of the controller for various controls, etc., cannot be quickly checked at their occurrences. A number of defective wafers are often produced.
Even when etching is conducted, and changes of etching characteristics are found on wafers, causes for the changes cannot be identified, and the system is often forced to be stopped for a long period of time.
This also happens in plasma processing systems for film deposition systems.